## Why
Windows sandbox provisioning performs privileged work beneath a requested Codex home. Provisioning paths and output entries must remain bound to the files and directories that were validated, without following reparse points or writing through caller-controlled hard links.
## What changed
- Add reusable no-reparse directory opens, path validation, directory guards, and handle-relative atomic file replacement.
- Use fresh or retained handles for provisioning logs, sandbox credentials, setup markers, and error reports in service provisioning mode.
- Add service-side validation for framed provisioning requests, proxy settings, fixed-drive Codex homes, and pinned sandbox directories.
## Testing
Add Windows tests covering junction and unsafe-path rejection, hard-link-safe output replacement, retained output handles, request framing and normalization, and ancestor pinning.
GitOrigin-RevId: 2ec4f0d15404c3387df1414bb0c1915cf452ecf2
johnl-oai
add870a4bf